Uterine and cytoplasmic effects on pup eyelid opening in two inbred strains of mice

Loss-of-function mutations in FREM2 disrupt eye morphogenesis

Cryptophthalmos is a rare congenital disorder characterized by ocular dysplasia with eyelid malformation. Complete cryptophthalmos is characterized by the presence of continuous skin from the forehead over the eyes and onto the cheek, along with complete fusion of the eyelids. In the present study, we characterized the clinical manifestations of three patients with isolated bilateral cryptophthalmos. These patients shared the same c.6499C > T missense mutation in the FRAS1-related extracellular matrix protein 2 (FREM2) gene, while each individual presented an additional nonsense mutation in the same gene (Patient #1, c.2206C > T; Patient #2, c.5309G > A; and Patient #3, c.4063C > T). Then, we used CRISPR/Cas9 to generate mice carrying Frem2^R725X/R2156W compound heterozygous mutations, and showed that these mice recapitulated the human isolated cryptophthalmos phenotype. We detected FREM2 expression in the outer plexiform layer of the retina for the first time in the cryptophthalmic eyes, and the levels were comparable to the wild-type mice. Moreover, a set of different expressed genes that may contribute secondarily to the phenotypes were identified by performing RNA sequencing (RNA-seq) of the fetal Frem2 mutant mice. Our findings extend the spectrum of FREM2 mutations, and provide insights into opportunities for the prenatal diagnosis of isolated cryptophthalmos. Furthermore, our work highlights the importance of the FREM2 protein during the development of eyelids and the anterior segment of the eyeballs, establishes a suitable animal model for studying epithelial reopening during eyelid development and serves as a valuable reference for further mechanistic studies of the pathogenesis of isolated cryptophthalmos.

Insensitivity of the analysis of variance to heredity-environment interaction

It makes sense to attribute a definite percentage of variation in some measure of behavior to variation in heredity only if the effects of heredity and environment are truly additive. Additivity is often tested by examining the interaction effect in a two-way analysis of variance (ANOVA) or its equivalent multiple regression model. If this effect is not statistically significant at the α = 0.05 level, it is common practice in certain fields (e.g., human behavior genetics) to conclude that the two factors really are additive and then to use linear models, which assume additivity. Comparing several simple models of nonadditive, interactive relationships between heredity and environment, however, reveals that ANOVA often fails to detect nonadditivity because it has much less power in tests of interaction than in tests of main effects. Likewise, the sample sizes needed to detect real interactions are substantially greater than those needed to detect main effects. Data transformations that reduce interaction effects also change drastically the properties ofthe causal model and may conceal theoretically interesting and practically useful relationships. If the goal ofpartitioning variance among mutually exclusive causes and calculating “heritability” coefficients is abandoned, interactive relationships can be examined more seriously and can enhance our understanding of the ways living things develop.

Maternal and genetic effects on the acoustic startle reflex and its sensitization in C3H/HeN, DBA/2JHd and NMRI mice following blastocyst transfer

In the present study, reciprocal embryo transfers were conducted to examine genetic and maternal effects on the baseline and fear-sensitized acoustic startle response (ASR) in the two inbred strains C3H/HeN and DBA/2JHd and the outbred strain NMRI. The largest differences in the ASR were found in untreated strains (effect size 0.6). The transfer procedure per se had a significant effect on the behavior of NMRI mice resulting in a reduction in the baseline, and an increase in the fear-sensitized ASR. In contrast, there were no significant effects of the transfer procedure in the two inbred strains. Autosomal genetic effects had a stronger impact on the amplitude of the ASR (effect sizes 0.5) than sex (effect sizes 0.06) as revealed by reciprocal embryo transfer. Nevertheless, the genetic effects on the fear-sensitized ASR were somewhat more variable and strain-dependent (effect sizes 0.1-0.2). Global maternal effects were detected after embryo transfer into NMRI mothers resulting in a larger reduction of the ASR in the offspring of DBA and NMRI donors than C3H donors (effect sizes 0.1-0.2). An additional fostering procedure was introduced to dissect uterine and postnatal maternal effects in NMRI offspring. Uterine factors changed the baseline ASR of the offspring in direction of the recipient mother strain. Surprisingly, postnatal maternal effects on the ASR were contrary to the behavior of the rearing mother. In conclusion, both genetic and prenatal/postnatal maternal factors persistently influenced the ASR of the offspring, whereas the fear-sensitized ASR was mainly influenced by genetic factors. Our study shows that uterine and postnatal maternal influences deserve more attention when determining the phenotype of genetically engineered mice at least in the first generation following embryo transfer.

Sensory and motor development in mice: genes, environment and their interactions

Sensory and motor developmental tests were designed to characterize spontaneous mutations in rodents. These tests are currently used to investigate developmental abnormalities associated with gene overexpression or gene targeting in mice. Here, we present an overview of our studies focused on 15 tests designed to measure sensory and motor development from birth to weaning in mice. Psychometric characteristics and factorial structure of these measures are considered first. The genetic correlates of these measures obtained with neurological mutants and gene mapping are compared. As a general rule, the contribution of genotype to the phenotypic variance of sensory and motor measures of development is low, inviting exploration of other sources of variation. Results from ovary transplantation, embryo transfer and fostering methods indicate that different components of maternal environment (cytoplasmic, uterine or postnatal) contribute to the behavioral phenotype. Although more difficult to detect, interactions between genotype and environment are involved.

Preweanling sensorial and motor development in laboratory mice: quantitative trait loci mapping

Chromosomal mapping of genes linked with 19 measures of sensorial, motor, and body weight development were investigated. Chromosomal mapping is the first step towards gene identification. When a genomic region is shown to be linked to a trait, it is possible to select a reduced number of candidate genes that have been previously mapped on this region. The involvement of every gene can be individually tested either by molecular (transgenesis, homologous recombination) or traditional methods (congenicity). Mapping was performed using 389 males and females from two inbred strains of laboratory mice C57BL/6By and NZB/BlNJ, their reciprocal F1s and F2s. Thirty-six Quantitative Trait Loci (QTL) were mapped, 12 reached the 3.13 lod score, being thus considered as confirmed. These QTL were tentatively labeled: Cliff Drop Aversion (Cliff Qtl), Geotaxia (Geot Qtl), Vertical Clinging (VertCling Qtl), Bar Holding with the 4 paws (BH4P Qtl), Age at Eyelid Opening (Aeyo Qtl), Visual Placing (Vispl Qtl), Startle Response (Start Qtl1, Start Qtl2), Body Weight at Day 10 in Males pooled with Females (Bwefmd10 Qtl), and Body Weight at Day 30 in males (Bwemd30 Qtl). For the majority of the developmental measures, the QTL that were mapped contributed little to the phenotypic variance, even when mitochondrial DNA contribution was included: Righting Response (12.7%), Cliff Drop Aversion (10%), Crossed Extensor Response (18.1%), Geotaxia (16.2%), Bar Holding Response for 10 s (12.1%), Bar Holding Response with 4 paws (8.1%), Vertical Clinging (9.3%), Vertical Climbing (5%), Startle Response (21.2%), Eyelid Opening (14.6%), Visual Placing (22%), Body Weight at Day 10 (27%), Body Weight at Day 15 in Females (52.5%), Body Weight at Day 15 in Males (17%), Body Weight at Day 30 in Females (42%), and Body Weight at Day 30 in Males (48%). A factorial analysis of the correlations between the measures of development did not provide evidence of a general factor. A general genetic factor of development was also rejected because few common genetic correlates were discovered for the 19 measures of development (Body Weight at Days 15 and 30 in Females on Chromosome 2, Eyelid Opening and Body Weight at Day 10 on Chromosome 5 and mitochondrial genome for five measures). Co-identification of genes, the function of which were previously known thanks to newly discovered QTL, should help to explain the function of QTL. Present data help to highlight candidate regions including several genes that could be candidates for the QTL function. Large confidence intervals were obtained as usual from the F2 intercrossed population. More stringent methods are suggested for more efficient co-identification.

The uterine environment enhances cognitive competence

Genetically identical mouse embryos were transferred into same-strain uteri (transfer controls) or into hybrid uteri. A third group was not transferred. When adult, the mice were given a series of behavioral tests. In-strain transfer controls differed from non-transfer mice only on two activity measures, and did not differ on any cognitive variable. In contrast, mice reared in hybrid uteri were found to be superior to in-strain transfer mice on discrimination learning. Lashley maze learning and Morris maze learning; they also showed better adaptation in an avoidance learning shuttlebox. To our knowledge this is the first study showing that the uterine environment can have a general enhancing effect upon cognitive competence across a broad range of behaviors.

The uterine environment enhances cognitive competence

Genetically identical mouse embryos were transferred into same-strain uteri (transfer controls) or into hybrid uteri. A third group was not transferred. When adult, the mice were given a series of behavioral tests. In-strain transfer controls differed from non-transfer mice only on two activity measures, and did not differ on any cognitive variable. In contrast, mice reared in hybrid uteri were found to be superior to in-strain transfer mice on discrimination learning, Lashley maze learning and Morris maze learning; they also showed better adaptation in an avoidance learning shuttlebox. To our knowledge this is the first study showing that the uterine environment can have a general enhancing effect upon cognitive competence across a broad range of behaviors.

Prenatal effects of parity on behavioral ontogeny in mice

In mice, parity and previous experience with pups may influence a mother's behavior towards her pups, thus possibly causing postnatal maternal effects on the subsequent development of the pups. The present experiment addressed the question whether parity also might have prenatal effects. We studied 622 pups from second or third litters that originated from 25 genetically different populations and had been fostered to random-bred lactating females. Development of responses was significantly delayed in mice from third litters, when compared to pups from second litters in three out of five sensorial and four out of eight motor tests. In addition, pups from second litters initially were slightly heavier than those from third litters. This difference in body weight disappeared after the 10th day postnatally. However, it should be noted that effect sizes were quite small.

Influence of the mother on development of aggressive behavior in male rats

The present experiments investigated pre- and postnatal maternal effects on aggressive behavior in rats. Resident-intruder aggressive behavior of male rats in colonies (two males and two females) was studied in five experimental groups: 1 = WWY (n = 7) the two males of each colony were wild (biological father and mother were wild) fostered by a wild mother; 2 = WAY (n = 11) the two males were wild fostered by an albino Wistar mother; 3 = AAY (n = 11) the two males were albino (biological father and mother were Wistar) fostered by an albino mother; 4 = AWY (n = 12) the two males were albino fostered by a wild mother; and 5 = HWX+HAX (n = 9) one of the males was hybrid born and reared by a wild mother (the father was albino) and the other was also hybrid but born and reared by an albino mother (the father was wild). Each test lasted 10 min and the intruder was always a Wistar male. Aggression of wild rats was higher than the laboratory ones, independently of the mother (albino or wild) they were fostered by. However, hybrid males born and reared by a wild mother were more aggressive than those that were born and reared by an albino mother, in spite of the father being wild. In conclusion, crossfostering has little effect on territorial aggression, but prenatal maternal effects seem to play a major role on the ontogeny of aggressive behavior of male rats.

In utero contiguity to males does not influence morphology, behavioral sensitivity to testosterone, or hypothalamic androgen binding in CF-1 female mice

Physiological and behavioral systems presumably influenced by prenatal exposure to testosterone (T) were compared in CF-1 female mice from known uterine positions. Anogenital distance did not differ among females that developed in utero between two females (0M), adjacent to one male (1M), or between two males (2M) at birth, at weaning on Day 21, or on Day 60 postpartum. The age of vaginal opening and mean estrous cycle length also were similar among the groups. When ovariectomized and implanted with a T-containing silastic capsule, the mean number of days of treatment required to activate male-like aggressive behavior also did not differ among the three positional classifications. Finally, androgen binding in combined hypothalamic-preoptic-septal cytosol was assessed after 8 days of T treatment, and no systematic variation in [3H]DHT binding related to uterine position was found. These results indicate that contiguity to male fetuses did not induce variation among CF-1 females in morphological, behavioral, or biochemical systems thought to be influenced by prenatal exposure to T.

beta-Carboline-induced seizures in mice: genetic analysis

The inbred mouse strains BALB/cBy (C) and C57BL/6By (B6) differed significantly in their susceptibility to seizures induced by the benzodiazepine inverse agonist methyl beta-carboline-3-carboxylate (beta-CCM). Following a 5 mg/kg injection of beta-CCM, 74% of C (n = 35) and 13% of B6 (n = 40) mice exhibited a convulsion. No sex difference was found. Analysis of the reciprocal F1s failed to show either maternal environmental and/or heterosomal effects. A genetic analysis of the strain difference in susceptibility to beta-CCM-induced seizures using recombinant inbred strains (RIS) was performed. The strain distribution for the RIS showed a two group partition. Statistical analysis showed that, although a one-segregating-unit model could not be rejected to explain the strain difference in beta-CCM-induced seizures, some of the evidence weakened the one-segregating-unit hypothesis.

Early development in mice. VI: Additive and interactive effects of offspring genotype and maternal environments

Ovarian transplantation (OT) and fostering (F) methods were used concomitantly to test for genotype effects and cytoplasmic, uterine and postnatal maternal effects on nine sensori-motor responses employed for measuring development in two inbred stains of mice: NZB (N) and CBA/H (H). Parental strain differences were observed for six responses: forelimb placing, hindlimb placing, visual placing, crossed extensor, vibrissae placing and bar holding. Reciprocal F1 comparison alone indicates a single H vs. N global maternal effect (visual placing), whereas the joint use of the OT and F methods shows a parental vs. F1 global maternal effect on parental pups for three responses (hindlimb placing, grasping and visual placing) and on F1 pups for two responses (forelimb placing and visual placing). Moreover, a postnatal maternal effect is reported for five responses; righting, forelimb placing, grasping, crossed extensor and visual placing. The effect of the maternal genotype via the uterine environment is observed for four responses: righting, fore- and hindlimb placing and visual placing. Genotypic effects are also demonstrated on fore-and hindlimb placing, bar holding and visual placing. These results confirm the absence of a general genetic factor and demonstrate the absence of a general environmental factor the rate of the early sensori-motor development.

Genetics and senescence. I. Age-related changes in activity and exploration in three inbred strains of mice

Exploratory, locomotor and ambulatory activities were measured in nine independent groups of three inbred strains of mice (BALB/cBy, C57BL/6J and DBA/2J), at three different ages (150 days, 400 days and 750 days). The results show that for two of the three variables, the age-related changes present different patterns as a function of strain. The genetic and/or environmental correlates of the reactivity to aging may thus depend on the behavioral trait under study.

Early development in mice: V. Sensorimotor development of four coisogenic mutant strains

Effects on sensorimotor development of four genes (at, Re, fz, and Wv) involved in coat color differences were investigated by employing four coisogenic strains of mice with the same genetic background C57BL/6JOrl (B6). Compared to wild-type B6, two mutations (fz and Wv) showed pleiotropic effects on development but the direction of these effects (delay or advance) differed in different tests. Body weight was decreased for each mutation. Heterozygosity vs. homozygosity at the W locus caused differences in crossed extensor, bar holding and female body weight. Epistatic effects between the at and Re genes were investigated by developing a double coisogenic strain, and were found for righting, hindpaw grasping, vibrissae placing responses and weight.